Machining fluid supply controlling system for a wire cut electrical discharge machine

ABSTRACT

A wire cut electrical discharge machine (10) has two machining fluid supply systems respectively for supplying machining fluid is having different qualities to the machining section (14) thereof, namely, a rough-machining fluid supply system (20) and a finish-machining fluid supply system (60). The rough-machining fluid supply system (20) has a first machining fluid quality regulating circuit comprising a first machining fluid tank (26) having a filtering device (3) for filtering powdery chips, a specific resistance detector (34), a cooler or heater (42, 44), an ion exchange device (52) and pumps (40, 58), and the finish-machining fluid supply system (60) has a second machining fluid quality regulating circuit comprising a second machining fluid tank (66), a specific resistance detector (74), an ion exchange device (92), a cooler or heater (42, 44) and pumps (40, 98). A machining fluid of a quality appropriate for the purpose of wire cut electrical discharge machining, namely, rough machining or finish machining, is supplied to the machining section.

DESCRIPTION

1. TECHNICAL FIELD

The present invention relates to a machining fluid supply controllingsystem for a wire cut electrical discharge machine and, moreparticularly, to a machining fluid supply controlling system for a wirecut electrical discharge machine, and capable of improving a finishingaccuracy of the wire cut electrical discharge machining.

2. BACKGROUND ART

It is well known that the quality of water having a high purity used asa machining fluid is closely related to the machining accuracy of thewire cut electrical discharge machining. The quality of the machiningfluid, i.e., water having a high purity, is adjusted according to themachining purpose. That is, the specific resistance of the machiningfluid is maintained at a comparatively low value for rough machining, inwhich a high discharge current is supplied to the wire cut electricaldischarge machine in order to avoid adhesion of powdery chips to thework, while the specific resistance of the machining fluid must bemaintained at a high value for a finishing wire cut electrical dischargemachining in which a low discharge current is supplied to the wire cutelectrical discharge machine, because the electrical discharge machiningaction is reduced due to current leakage when the specific resistance ofthe machining fluid is small.

However, no single conventional wire cut electrical discharge machinehas been able to integrally and efficiently carry out rough machiningthrough finish machining by simply changing the quality, particularly,the specific resistance, of the machining fluid for rough machining andfor finish machining. Therefore, it has been necessary to use separatewire cut electrical discharge machines for rough machining and forfinish machining respectively.

Accordingly, it is an object of the present invention to provide amachining fluid supply controlling system for a wire cut electricaldischarge machine, capable of readily changing the specific resistanceof the machining fluid between a level appropriate for rough machiningand a level appropriate for finish machining when controlling thequality of the machining fluid, to enable a single wire cut electricaldischarge machine to integrally carry out the rough machining throughfinish machining.

DISCLOSURE OF THE INVENTION

The present invention provides a machining fluid supply controllingsystem for a wire cut electrical discharge machine having arough-machining fluid supply system for rough machining and afinish-machining fluid supply system for finish machining, which areconnected to the machining section of the wire cut electrical dischargemachine, and capable of supplying machining fluids respectively havingdifferent qualities respectively for rough machining and for finishmachining. The system comprises a first machining fluid tank having afiltering device and provided in the rough-machining fluid supplysystem. A second machining fluid tank has a filtering device and isprovided in the finish-machining fluid supply system. A first machiningfluid supply passage a pressurized machining fluid from the firstmachining fluid tank to the machining section. A second machining fluidsupply passage supplies a pressurized machining fluid from the secondmachining fluid tank to the machining section. First and second returnpassages return the machining fluid from the machining sectionrespectively to the first and second machining fluid tanks. A firstmachining fluid quality regulating circuit regulates the quality of themachining fluid to be supplied under pressure from the first machiningfluid tank to the machining section. A second machining fluid qualityregulating circuit regulates the quality of the machining fluid to besupplied under pressure from the second machining fluid tank to themachining section.

Preferably, the first machining fluid quality regulating circuit and thesecond machining fluid quality regulating circuit are providedrespectively with specific resistance detectors, each for detecting thespecific resistance of the associated machining fluid, respectively withflow regulating valves each capable of varying in opening degreeaccording to the specific resistance of the machining fluid detected bythe corresponding specific resistance detector, and respectively withion exchange devices for increasing the specific resistance of themachining fluid. The second machining fluid tank has a capacity smallerthan that of the first machining fluid tank. The machining fluids aresupplied respectively through the first and second machining fluidsupply passages by a pump under substantially the same pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description takenin conjunction with the accompanying drawing, in which:

FIG. 1 is schematic block diagram of a machining fluid supplycontrolling system for a wire cut electrical discharge machine, in apreferred embodiment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, enclosed by dotted lines and generally indicated at10 is an electrical discharge machine provided with a machining section14 having a machining fluid jetting unit including an upper nozzle 12aand a lower nozzle 12b. A machining fluid spouted into the machiningsection 14 is collected in a receptacle 16 for recovery. The machiningfluid collected in the receptacle 16 is returned to a first machiningfluid tank or to a second machining fluid tank included in the machiningfluid supply controlling system, which will be described afterward. Themachining fluid thus recovered is subjected to a regenerating processfor removing powdery chips and adjusting or improving the quality, andthen the regenerated machining fluid is supplied again to the machiningsection 14.

The machining fluid supply controlling system has a rough-machiningfluid supply system 20 and a finish-machining fluid supply system 60.The used machining fluid can be returned from the receptacle 16 of theelectrical discharge machine 10 through a first machining fluid returnpassage 24 provided with a shutoff valve 22 to the first machining fluidtank 26, or from the receptacle 16 through a second machining fluidreturn passage 64 provided with a shutoff valve 62 to the secondmachining fluid tank 66. The first machining fluid tank 26 of therough-machining fluid supply system 20 is provided internally with afiltering device 30 having filter elements 28a and 28b. The usedmachining fluid returned from the receptacle 16 is circulated throughthe filtering device 30 by a pump (P₂) 32 to remove powdery chips fromthe machining fluid. The discharge port of the pump 32 is connected alsoto the first machining fluid tank 26 to avoid overloading the pump 32due to the circulation of the machining fluid through the filteringdevice 30 at an excessive flow rate. After removing powdery chips fromthe machining fluid by the filtering device 30, the machining fluid ispumped by a pump (P₃) 40 so as to flow through a passage 36a providedwith a specific resistance detector 34, a shutoff valve 38, the pump 40,a cooler 42, a heater 44, a manual shutoff valve 46, shutoff valves 48and 50, and an ion exchange device (1E-1) 52 to regulate the fluidtemperature and to improve the quality, such as the level of specificresistance, by improving the purity of the machining fluid. Themachining fluid thus treated is returned to the first machining fluidtank 26. While the specific resistance of the machining fluid detectedby the specific resistance detector 34 is maintained at a value above afixed level, the shutoff valve 50 is held closed by applying a signalthrough a suitable signal line to the shutoff valve 50, and the shutoffvalve 48 is opened so that the machining fluid is returned through thepassage 36a directly to the filtering device 30 of the first machiningfluid tank 26. The pump 40 is a pressurizing means for pumping themachining fluid under pressure through the passage 36a. The temperatureof the machining fluid contained in the first machining fluid tank 26 isdetected by a temperature detector 54, and either the machining fluidcooler 42 or the machining oil heater 44 is operated depending on thedetected temperature of the machining fluid. The regenerated machiningfluid is supplied under pressure through a passage 36b provided with acheck valve 56 to the machining section of the wire cut electricaldischarge machine 10 by a pump (P₁) 58. While the machining fluid issupplied to the machining section 14 by the rough-machining fluid supplysystem 20, a manual shutoff valve 59 is closed to stop the supply ofmachining fluid by the finish-machining fluid supply system 60.

The second machining fluid tank 66 of the finish-machining fluid supplysystem 60 is provided internally with a filtering device 70 having afilter element 68. The recovered machining fluid is circulated throughthe filtering device 70 by a pump (P₅) 72 similarly to circulating therecovered machining fluid through the filtering device 30 provided inthe first machining fluid tank 26 of the rough-machining fluid supplysystem. It is a constitutional feature of this embodiment that a passage76a provided with a specific resistance detector 74 and a shutoff valve78 is coupled with the passage 36a of the rough-machining fluid supplysystem 20 after the shutoff valve 78 by the fluid couples 110 and 112.The passages 36a and 76a are coupled together by the fluid couplers 110and 112 to enable use of the pump 40, the machining fluid cooler 42 andthe machining fluid heater 44 for both the rough-machining fluid supplysystem 20 and the finish-machining fluid supply system 60. Thefinish-machining fluid is pumped by the pump 40 through the machiningfluid cooler 42, the machining fluid heater 44, the manual shutoff valve86, shutoff valves 88 and 90, and an ion exchange device (1E-2) 92 toreturn the finish-machining fluid to the second machining fluid tank 66after regulating the quality thereof. While the purity, i.e., thespecific resistance, of the finish-machining fluid detected by thespecific resistance detector 74 is maintained at a value above apredetermined level, the shutoff valve 90 provided immediately beforethe ion exchange device 92 is closed to return the finish-machiningfluid through the shutoff valve 88 directly into the filtering device 70of the second machining fluid tank 66. On the other hand, theregenerated finish-machining fluid is supplied under pressure throughcheck valves 96 and 100 and the manual shutoff valve 59 provided in apassage 76b by a pump (P₄) 98 to the machining section 14 of the wirecut electrical discharge machine 10. A temperature detector 94 similarto the temperature detector 54 is provided in the second machining fluidtank 66.

The machining fluid supply controlling system which regulates thequality of the machining fluid, regenerates the used machining fluid andsupplies the regenerated machining fluid to the rough-machining fluidsupply system 20 and the finish-machining fluid supply system 60 isconstituted generally as described above. The rough-machining fluidsupply system 20 has a first machining fluid quality regulating circuitfor regulating the quality of the machining fluid, including thespecific resistance detector 34, the machining fluid cooler 42, themachining fluid heater 44, and the ion exchange device 52, and amachining fluid supply passage provided with the pump 58, while thefinish-machining fluid supply system 60 has a second machining fluidquality regulating circuit for regulating the quality of the machiningfluid, including the specific resistance detector 74, the machiningfluid cooler 42, the machining fluid heater 44, and the ion exchangedevice 92, and a machining fluid supply passage provided with the pump98.

In accordance with the present invention, the capacity of the secondmachining fluid tank 66 of the finish-machining fluid supply system 60is comparatively small compared with that of the first machining fluidtank 26, and thus the quantity of the finish-machining fluid used in themachining fluid supply controlling system is smaller than that of therough-machining fluid used in the same. Accordingly, the rate of qualityregulation of the finish-machining fluid is higher than that of therough-machining fluid when the pumps 58 and 98 have substantially thesame discharge capacity to maintain the flow rate of the machining fluidin the rough-machining fluid supply system 20 and that of the machiningfluid in the finish-machining fluid supply system 60 during wire cutelectrical discharge machining at substantially the same rate, becausethe pump 40 is used both for supplying the rough-machining fluid and forsupplying the finish-machining fluid. That is, supposing that thequantity of the finish-machining fluid reserved in the second machiningfluid tank 66 is one-half or one-third the quantity of therough-machining fluid reserved in the first machining fluid tank 26, onerough-machining fluid supply cycle in which the total quantity of therough-machining fluid reserved in the first machining fluid tank 26 issupplied to the machining section 14, returned to the first machiningfluid tank 26, and subjected to the quality regulating treatmentcorresponds to two or three finish-machining fluid supply cycles inwhich the total quantity of the finish-machining fluid is supplied tothe machining section 14, returned to the second machining fluid tank 66and subjected to the quality regulating treatment two or three times.Accordingly, although the frequency of finish-machining fluidcirculating cycles for circulating the finish-machining fluid throughthe machining section 14 is higher than that of the rough-machiningfluid circulating cycles, the finish-machining fluid can be maintainedat a fixed temperature and the specific resistance of thefinish-machining fluid can be maintained at a fixed high level to ensurehighly accurate finish machining. While the rough-machining fluid supplysystem 20 is operative, the shutoff valves 62, 78, 88 and 90 and themanual shutoff valves 59 and 86 are closed and the pumps 72 and 98 arestopped. While the finish-machining fluid supply system 60 is operative,the shutoff valves 22, 38, 48 and 50 and the manual shutoff valve 46 areclosed and the pumps 32 and 58 are stopped.

As apparent from the foregoing description of the present invention withreference to the preferred embodiment, according to the presentinvention, a single wire cut electrical discharge machine is providedwith a rough-machining fluid supply system and a finish-machining fluidsupply system which can be changed over from one to the other accordingto the purpose of the machining process, and the rough-machining fluidsupply system and the finish-machining fluid supply system are providedrespectively with machining fluid quality regulating circuits tostabilize the temperature of the machining fluid and to maintain thespecific resistance of the machining fluid on a level appropriate forthe purpose of the machining process for effective quality regulation.Furthermore, the machining fluid supply controlling system of thepresent invention is capable of maintaining the specific resistance ofthe machining fluid at a high level necessary for the finish machiningprocess to enhance the finish machining accuracy of the wire cutelectrical discharge machine compared with that of the conventional wirecut electrical discharge machine.

We claim:
 1. A machining fluid supply controlling system for a wire cutelectrical discharge machine having a rough-machining fluid supplysystem and a finish-machining fluid supply system, which are connectedto the machining section thereof, capable of supplying machining fluidsrespectively having different qualities respectively for rough machiningand for finish machining, said machining fluid supply controlling systemcomprising:a first machining fluid tank having a filtering device andprovided in the rough-machining fluid supply system; a second machiningfluid tank having a filtering device and provided in thefinish-machining fluid supply system; a first machining fluid supplypassage through which a machining fluid is supplied under pressure fromthe first machining fluid tank to the machining section; a secondmachining fluid supply passage through which a machinig fluid issupplied under pressure from the second machining fluid tank to themachining section; first and second machining fluid return passages forreturning the machining fluid respectively to the first and secondmachining fluid tanks; a first machining fluid quality regulatingcircuit for regulating the quality of the machining fluid to be suppliedunder pressure from the first machining fluid tank to the machiningsection including means for detecting the specific resistance of thefirst machining fluid, an ion exchange device for increasing thespecific resistance of the first machining fluid and a flow controlvalve which opens in response to a detected specific resistance of thefirst machining fluid below a predetermined level to permit said firstmachining fluid to flow to said ion exchange device; and a secondmachining fluid quality regulating circuit for regulating the quality ofthe machining fluid to be supplied under pressure from the secondmachining fluid tank to the machining section including means fordetecting the specific resistance of the second machinig fluid, a secondion exchange device for increasing the specific resistance of the secondmachining fluid and a second flow control valve which opens in responseto a detected specific resistance of the second machining fluid below apredetermined level to permit said second machining fluid to flow tosaid second ion exchange device.
 2. A machining fluid supply controllingsystem for a wire cut electrical discharge machine, according to claim1, wherein said first and second machining fluid quality regulatingcircuits further include a pair of fluid couplers interconnecting thefirst and second machining fluid quality regulating circuits, a commonpassage provided with a machining fluid cooler and a machining fluidheater therein, and two manual shutoff valves to shut off one and toopen the other of the first and second machining fluid qualityregulating circuits.
 3. A machining fluid supply controlling system fora wire cut electrical discharge machine, according to claim 2, whereinsaid first and second machining fluid tanks are provided respectivelywith temperature detectors, and the machining fluid cooler or themachining fluid heater provided in the common passage is operateddepending on the temperature of the machining fluid detected by thetemperature detectors.
 4. A machining fluid supply controlling systemfor a wire cut electrical discharge machine, according to claim 1,wherein the capacity of said second machining fluid tank is smaller thanthat of the first machining fluid tank, and said machining fluids aresupplied under substantially the same pressure to the machining sectionrespectively through said first and second machining fluid supplypassages by a pump means.